I. Field of the Invention
This invention relates to anaerobic curing compositions utilizing polymerizable acrylic and substituted acrylic monomers together with an alpha-hydroxy sulfone catalyst to effect latent polymerization of the acrylic monomers. The compositions are stable for periods of time extending to a half-year or more in the presence of air or oxygen, but cure rapidly when placed between air or oxygen impermeable surfaces such as metal, glass, etc. thereby finding use as anaerobic adhesives and sealants. Further, the addition of certain dialkyl peroxides to these novel compositions has been found to result in an adhesive having substantially increased shear strength and longer shelf life.
II. Brief Description of the Prior Art
Anaerobic curing compositions are known and well described in the prior art. U.S. Pat. No. 2,628,178 issued Feb. 10, 1953 describes the preparation of anaerobic curing compositions which rely on the oxygenation of certain monomers until at least 0.1% of active oxygen is introduced into the monomer. The oxygenated monomer remains stable until polymerization is initiated by the absence of air. Another patent, U.S. Pat. No. 2,895,950 issued July 21, 1959, describes compositions containing defined polymerizable polyacrylate ester monomers together with hydroperoxide catalysts. Later patents dealing with anaerobic curing sealants disclose the use of stabilizers, accelerators, etc. in conjunction with peroxide, perester or hydroperoxide catalysts. Recently, U.S. Pat. No. 3,775,385 as well as U.S. Pat. No. 3,880,956 assigned to the assignee of the present application, have disclosed alternate catalysts which do not require the presence of the peroxidic class of compounds.
The use of alpha-hydroxy sulfones as accelerators for peroxides in redox systems has been described, however, there has heretofore been no indication that these sulfones would function without the necessity of peroxides as satisfactory catalysts for the curing of acrylic monomeric compositions in an anaerobic environment.